An embodiment of the present invention relates generally to sensing edges for motorized closures, and more particularly, to a combination contact and non-contact sensing edge.
Contact sensing edges for automatic closures (e.g., doors, gates, windows, and the like) are generally well known. A description of such sensing edges can be found, for example, U.S. Pat. No. 5,089,672, entitled “Flexible Electrically Conductive Contact for a Switch which is Actuated Upon Force Being Applied Thereto,” and U.S. Pat. No. 6,571,512, entitled “Universal Sensing Edge with Non-Melt End Closure,” the entire contents of each of which are incorporated by reference herein.
Such sensing edges generally include an elongate sheath in which a force sensing switch (sensor) is positioned. Upon the application of an undesired force to the sheath, the sensor actuates suitable control circuitry for controlling movement of, for example, a door. The sensor, positioned within the sheath, typically comprises a pair of electrically conductive, preferably flexible, elements that are ordinarily physically and electrically separated from one another. The conductive elements may be wires, foils, conductive polymers, or the like. The conductive elements may be physically separated by air, but other materials may be used to ensure the separation, such as a perforated foam or other permeable non-conductive material. Upon application of force to the sheath, the two conductive elements are forced into contact, reducing resistance between the two conductive elements from a very high value to a very small value. The system interprets this condition as the presence of an obstacle, which signals the motor controller to act accordingly.
Proximity or non-contact sensors are also generally known. Such sensors generally include a sensing antenna that is connected to a self-resonating oscillator and which generates an electric field in a region of the sensor. The proximity of conductive objects in the field changes the oscillator's frequency. When the frequency changes by a threshold amount, an object in the field is “sensed,” and suitable control circuitry may be actuated to provide an alarm or to undertake measures to avoid contact with the sensed object. An early method of non-contact sensing was described in U.S. Pat. No. 1,661,058, which taught an instrument that could generate audible sound tones in response to changes in proximity of a human hand (acting as a ground plate of a variable capacitor) to an oscillating system.
As with any such device, there is an assumption of an earth-ground connection to the environment. Closures are typically connected to ground through rails and/or posts. In addition, the leading edge of a door commonly has a metal bar. It is necessary for the oscillator circuit in such a system to be connected to this common ground. Any shields must also be connected to the circuit ground or an equivalent earth-ground.
Contact sensing edges have the drawback that contact must necessarily be made with an object in order to activate the safety response of the door. While non-contact sensors can overcome this drawback with respect to conductive objects, such as individuals or metal objects, non-conductive materials (e.g., paper, wood, plastic, or the like) are not accurately detectable by this method. Thus, it is desirable to provide a door or other motorized closure with both contact and non-contact sensing capabilities. Attempts have been made in this regard. However, the contact and non-contact sensors were separate from one another. Such combinations are more complex and expensive to implement.
It is therefore desirable to provide a combination contact and non-contact sensing edge that is simple to implement without changing the design of the sensing edge.